Tire with circumferentially zoned tread including stratified lateral zones and peripheral sidewall extensions

ABSTRACT

The invention relates to a tire having a rubber tread of a circumferentially zoned tread including stratified lateral tread zones and peripheral sidewall extensions. The tread zones are comprised of three circumferential load bearing zones, with each zone containing a portion of the running surface of the tread, comprised of an intermedial zone positioned between and two stratified lateral tread zones together and, in addition, peripheral sidewall extensions. The intermedial and stratified lateral zones are comprised of rubber compositions having differentiated 100° C. hot rebound physical properties. The intermedial rubber zone, or layer, overlays a tread base rubber layer and underlies the lateral tread layer zones. The lateral tread zones are stratified in a sense of being separated from each other and also separated from the from the tread base rubber layer by the intermedial rubber layer. The tread includes a peripheral carbon black rich rubber layer as a sidewall extension which extends radially outward from the outer tire sidewall to thereby join a portion of the peripheral tread zone rubber layer and extends to and includes a portion of the running surface of the tread.

The invention relates to a tire having a rubber tread of acircumferentially zoned tread including stratified lateral tread zonesand peripheral sidewall extensions. The tread zones are comprised ofthree circumferential load bearing zones, with each zone containing aportion of the running surface of the tread, comprised of an intermedialzone positioned between and two stratified lateral tread zones togetherand, in addition, peripheral sidewall extensions. The intermedial andstratified lateral zones are comprised of rubber compositions havingdifferentiated hot rebound physical properties. The intermedial rubberzone, or layer, overlays a tread base rubber layer and underlies thelateral tread layer zones. The lateral tread zones are stratified in asense of being separated from each other and also separated from thetread base rubber layer by the intermedial rubber layer. The treadincludes a peripheral carbon black rich rubber layer as a sidewallextension which extends radially outward from the outer tire sidewall tothereby join a portion of the peripheral tread zone rubber layer andextends to and includes a portion of the running surface of the tread.

BACKGROUND FOR THE INVENTION

Tire treads for pneumatic tires typically have running surfaces of aunitary rubber composition and therefore rubber properties attributed tothe tread rubber composition across the face of the tread. The tread isusually composed of a lug and groove configuration composed ofground-contacting lugs with intervening grooves between the lugs.

Tires intended for heavy duty, in a sense of carrying large loads, suchas for example truck tires, are typically intended to experienceinternal heat generation during the service, or operation, of the tireand to experience considerable stress at peripheral outer, or lateral,portion(s) of the tread, including tread grooves contained in thetread's ground-contacting stratified lateral zones due to, for example,vehicular cornering and tire scuffing against roadside objectsincluding, for example, roadside curbs. When such tire stress isexcessive, a surface cracking of a surface of a groove wall contained ina stratified lateral zone of the tread may occur in response to theconsiderable stress.

The outer, ground-contacting, tread cap rubber layer is typicallycomprised of a relatively low hysteretic rubber composition to promoterelatively low internal heat generation as the tire is used in serviceas evidenced by relatively high rubber rebound and relatively low tandelta physical properties to, in turn, thereby promote a low rollingresistance of the tire tread as well as extended tread shoulder groovedurability.

For this invention, it is proposed to provide the outer tread cap rubberlayer in a form of circumferential zones of significantly differentphysical properties, particularly rubber compositions of differingphysical properties such as hot rebound (100° C.) properties which areindicative of hysteresis of the rubber composition and predictive ofrate of internal heat generation during use of the tire and alsopredictive of rolling resistance of the tire. For this invention, suchtread zones are provided as an intermedial rubber zone to promote lowerhysteresis with resultant lower internal heat build-up across thebreadth of the tire tread positioned between and underlying lateral,stratified rubber zones.

In particular, it is proposed to provide the intermedial rubber zone,which extends across the underlying tread base rubber layer, with ahigher 100° C. hot rebound property, thereby a lower hysteresisproperty, than the stratified overlying lateral tread zones to promote arelative maximization of reduced internal heat build-up within thetread. The stratified lateral tread zone rubber composition is thereforeproposed to have a relatively lower 100° C. hot rebound property,thereby a higher hysteresis. It is further desired for the lateral treadzone rubber composition to have a greater or equal, preferably greatertear resistance property compared to the intermedial tread zone rubber,particularly to reinforce tread grooves contained in the stratifiedlateral tread zones.

Historically, tires have heretofore been proposed having an outersurface composed of a plurality of circumferential zones of rubbercompositions to promote various properties for the tread's runningsurface.

For example, see U.S. Pat. Nos. 8,662,123; 7,789,117; 7,559,348;7,131,474 and 6,959,744; Patent Publication Nos. 2007/0017617 and2009/0107597; EP0718127, EP0798142 and DE19812934.

However, it is hereby proposed to provide a tire with tread containing aplurality of circumferential zones of rubber compositions to promotesignificantly different physical properties to include reboundproperties to therefore promote differentiated hysteresis propertiestogether with a peripheral sidewall extension rubber layer. Thedifferentiated rebound properties (e.g. hysteresis properties) for thetread zones is desired to promote, or maximize, a beneficially lowerinternal heat buildup for the tread.

In this manner then, the central portion of the tread is a dual layeredcomposite of an intermedial tread cap rubber zone layer and tread baserubber layer. The lateral portions of the tread are triple layeredcomposites of the stratified rubber zones, the portion of theintermedial tread zone which extends beneath and underlies the lateraltread zones and the tread base rubber layer which underlies theintermedial tread zone.

The tire tread it thereby comprised of a cooperative layered compositeof the aforesaid circumferential rubber layers.

In one embodiment, tread grooves are contained in both the intermedialtread zone and the lateral tread zones. By providing the lateral treadzone rubber layers with a tear resistance property, it is intended thattear resistance of the surface of the grooves contained in the lateralportion of the tread is promoted.

In the description of this invention, the terms “rubber” and “elastomer”may be used interchangeably, unless otherwise provided. The terms“rubber composition”, “compounded rubber” and “rubber compound” may beused interchangeably to refer to “rubber which has been blended or mixedwith various ingredients and materials” and such terms are well known tothose having skill in the rubber mixing or rubber compounding art. Theterms “cure” and “vulcanize” may be used interchangeably unlessotherwise provided. The term “phr” may be used to refer to parts of arespective material per 100 parts by weight of rubber, or elastomer.

SUMMARY AND PRACTICE OF THE INVENTION

In accordance with this invention, a tire is provided having acircumferential rubber tread composed of a cap/base configurationcomprised of an outer tread cap rubber layer with a lug and grooveconfiguration with the outer portions of the tread lugs providing therunning surface of the tread, and a tread base rubber layer underlyingthe outer tread cap rubber layer;

wherein the outer tread cap rubber layer is composed of threecircumferential load bearing zones comprised of an intermedial treadzone rubber layer positioned between and extending beneath two lateraltread zone rubber layers to thereby underlie the lateral tread zonerubber layers and overlay the tread base rubber layer to thereforestratify the lateral tread zone rubber layers as being separated fromeach other and from the tread base rubber layer;

wherein outer lug surfaces of the intermedial tread zone rubber layerand surfaces of the lateral tread zone rubber layers comprise therunning surface of the tread;

wherein a peripheral rubber layer of the tread is provided which iscomprised of a radial extension of a tire sidewall rubber layercontaining at least about 40 phr of rubber reinforcing carbon blackwhich extends radially outward from the tire sidewall to form aperipheral rubber layer of the tread which extends to and includes aportion of the running surface of the tire;

wherein rubber composition of the intermedial tread zone rubber layerhas a 100° C. hot rebound property greater than the 100° C. hot reboundproperty of the rubber composition of the stratified lateral treadrubber layers.

In one embodiment, the value of the 100° C. hot rebound property of theintermedial tread zone rubber composition is at least about 4 unitsgreater than the 100° C. hot rebound property value of the stratifiedlateral tread zone rubber composition.

For example, the 100° C. hot rebound value of the intermedial tread zonerubber composition may be in arrange of from about 60 to about 80percent and the 100° C. hot rebound value of the rubber composition ofthe stratified lateral tread zone rubber composition may be in a rangeof from about 56 to about 76 so long as the 100° C. rebound valuesdiffer by at least about 4 units (e.g. percentage units, for example, ahot rebound value of 80 percent for the intermedial zone rubbercomposition and hot rebound value of 76 percent, or less, for thestratified lateral tread zone rubber composition).

In one embodiment, it is further desired for the stratified lateraltread zone rubber composition to have a greater or equal, preferablygreater, tear resistance property than the intermedial tread zonerubber.

The particulate reinforcement of the rubber compositions of theintermedial tread rubber zone and stratified lateral tread rubber zonesmay be the same or different and comprised of rubber reinforcing carbonblack and/or precipitated silica reinforcement so long as the 100° C.hot rebound property of the rubber composition of the intermedial treadrubber zone is greater than the 100° C. hot rebound property of therubber composition of the stratified lateral rubber zones.

The elastomers of the rubber compositions of the intermedial treadrubber zone and stratified lateral tread rubber zones may be the same ordifferent so long as the 100° C. hot rebound property of the rubbercomposition of the intermedial tread rubber zone is greater than the100° C. hot rebound property of the rubber composition of the stratifiedlateral rubber zones.

For example, in one embodiment, the rubber composition of theintermedial zone and/or stratified lateral tread zones may besilica-rich in a sense of containing at least 40 phr of precipitatedsilica and a maximum of 30 phr of rubber reinforcing carbon black andthereby presenting a significant degree of insulative electricalresistance for the intermedial and/or lateral rubber layer zones so longas the 100° C. hot rebound property of the intermedial tread zone isgreater than the 100° C. hot rebound property of the stratified treadzones. In such case, the peripheral carbon black-rich rubber sidewallextension may assist in providing a path of least electrical resistancebetween the tire carcass and tread running surface.

For example, in one embodiment the rubber composition of the intermedialzone and/or stratified lateral zones may be carbon black rich in a senseof containing at least 40 phr of rubber reinforcing carbon black zonesso long as the 100° C. hot rebound property of the intermedial treadzone is greater than the 100° C. hot rebound property of the stratifiedtread zones.

In one embodiment, the span of the running surface of the intermedialtread zone rubber layer axially spans from about 30 to about 80 percentof the running surface of the tread cap rubber layer and the twostratified lateral tread rubber zone rubber layers collectively spanfrom about 20 to about 70 percent of the running surface of the treadcap rubber layer where said span of running surface of the treadincludes the running surfaces of the tread lugs and widths of the treadgrooves between the tread lugs.

In one embodiment, the span of the running surfaces of the twoindividual stratified lateral tread zones may be of equal widths, or atleast of substantially equal widths, or may be asymmetrical in a sensethat they are of unequal widths, namely, for example, of widths withinabout 80 to about 120 percent of each other.

As indicated, the span of the running surface of the tread cap layerincludes the outer running surface of the tread lugs (intended to beground contacting) and the width of the included grooves between thelugs.

In one embodiment, the Grosch abrasion rate (e.g. Grosch high abrasionrate) of the rubber composition of the running surfaces of theintermedial tread rubber layer and stratified lateral tread zone rubberlayers are desirably similar. For example, in one embodiment theirGrosch abrasion rates may be within about 5 to 20 percent of each other.

In one embodiment, the tear resistance (Newtons at 95° C.) of the rubbercomposition of the stratified lateral tread zones is at least 20 percentgreater than the tear resistance of the rubber composition of theintermedial tread zone.

In one embodiment, the stratified lateral tread zones, intermedial treadzone and underlying tread base are co-extruded together to form anintegral and unified tread composite.

In one embodiment, the rubber of the intermedial, tread cap zone has alower tan delta value at 10 percent strain (100° C.) than the rubber ofthe two lateral tread cap zones which is predictive of lower hysteresiswhich is, in turn, predictive of lower internal heat buildup during tireservice and a beneficially lower rolling resistance contribution of theintermedial tread cap rubber layer for the tire.

Accordingly, it is an aspect of this invention to provide a significantbalance of physical properties of rubber compositions between theintermedial tread zone and stratified lateral tread zones in a manner ofbeing a departure from past practice.

It is to be appreciated that one having skill in rubber compounding fortire treads can readily provide the tread zones with the indicatedrubber composition properties with routine experimentation and withoutundue experimentation.

BRIEF DESCRIPTION OF THE DRAWINGS

Drawings are presented to provide a further understanding of theinvention. In the Drawings, FIG. 1 (FIG. 1) is provided to illustrate apartial cross sectional view of a tire with a circumferential tread of acap/base configuration where the outer cap rubber layer is divided intothree circumferential tread zones, namely two spaced apart lateral treadzones and an intermedial tread zone of which a portion extends in anaxially outward direction from each side of the intermedial tread zonebeneath the lateral tread zones and adjoins and separates the lateraltread zones from each other and from the tread base rubber layer tothereby stratify the lateral tread zones. A carbon black richtread-protective rubber sidewall extension is also provided whichextends radially outward from the outer tire sidewall to thereby join aportion of the stratified lateral tread zone rubber layer and extends toand includes a portion of the running surface of the tread which mayalso thereby provide a path of electrical conductivity to a runningsurface of the tire.

THE DRAWINGS

In the Drawings, FIG. 1 illustrates a pneumatic tire partial crosssection (1) having a tread (2) of a cap/base configuration, namely anouter tread cap rubber layer (3) of a lug and groove configuration andan underlying tread base rubber layer (4). The outer tread cap rubberlayer (3) contains tread running surfaces (not numbered) contained onthe outer surfaces of the tread lugs of the tread (2) and is composed ofthree circumferential tread zones, each a part of the tread's runningsurface, comprised of an intermedial tread zone rubber layer (6) betweentwo spaced apart individual lateral tread zones (5A) and (5B) of whichportions (6A) and (6B) of the intermedial tread zone (6) extend beneathand thereby underlie both of the lateral tread zones (5A) and (5B) andalso overlay the tread base rubber layer (4). The outlying lateral treadzones (5A) and (5B) are thereby stratified in a sense being spaced apartfrom each other and spaced apart from the tread base rubber layer (4).The tread base rubber layer (4) thereby underlies the intermedial treadzone rubber layer (6) and is exclusive of the lateral tread zones (5A)and (5B). The lateral tread zones (5A) and (5B) are shown as being ofthe same width although they may be of widths which differ from eachother.

The tread lug and groove configuration provides tread lugs withintervening grooves with grooves (7) contained in the intermedial treadzone layer (6) and grooves (7A) and (7B) contained in the stratifiedlateral tread zone layers (5A) and (5B) with each of the stratifiedlateral tread zones thereby containing at least one tread groove. Forsuch purpose it is desired that the stratified tread zone layer rubbercompositions have a significantly greater tear resistance property thanthe intermedial zone layer rubber composition to thereby aid inprotecting the tread grooves (7A) and (7B) contained in the stratifiedlateral tread zone layers (5A) and (5B).

A carbon black rich rubber sidewall extension (9) containing at least 40phr of rubber reinforcing carbon black extends radially outward from theouter tire sidewall to the tire tread (2) to become a peripheral outerrubber layer of the tire tread (2) thereby join a portion of the lateraltread zone rubber layers (5A) and/or 5(B) and extends to and includes aportion of the running surface (not numbered) of the tread (2) tothereby aid in protecting the tread grooves (7B) which may provide apath of electrical conductivity (reduced electrical resistance) to arunning surface (not numbered) of the tire (1), particularly where theintermedial tread zone (6) is of a silica-rich rubber composition whichcontains a maximum of 30 phr of rubber reinforcing carbon black.

For FIG. 1, the intermedial tread zone (6) is depicted as constitutingabout 45 to 60 percent of the spanned running surface of the tire tread(2) and the two individual lateral tread zone layers (5A) and (5B) areof a substantially equal width and correspondingly collectivelyconstitute about 55 to about 40 percent of the spanned running surfaceof the tire tread (2).

For exemplary FIG. 1, the intermedial and stratified lateral tread zonerubber compositions may be comprised of the same or different elastomersand contain the same or different reinforcing fillers selected fromrubber reinforcing carbon black and precipitated silica so long as the100° C. hot rebound property of the intermedial zone rubber is greaterthan that of the stratified later zone rubbers.

As indicated, the span of the running surface of the tread cap layerincludes the outer running surface of the tread lugs (intended to beground contacting) and the width of the included grooves between thelugs.

For exemplary FIG. 1, the tread base layer may, for example, beprimarily comprised of either cis 1,4-polyisoprene rubber, preferablynatural rubber, or a combination of the cis 1,4-polyisoprene rubber anda polybutadiene rubber selected from cis 1,4-polybutadiene rubber andtrans 1,4-polybutadiene rubber. Optionally, also it may also contain upto about 20 phr (e.g. from about 5 to about 15 phr) of at least oneadditional conjugated diene based elastomer such as, for example, atleast one additional diene-based elastomer selected from at least one ofstyrene/butadiene rubber, isoprene/butadiene rubber, trans1,4-polybutadiene, low vinyl polybutadiene having vinyl content in arange of 10 to about 40 percent, and styrene/isoprene/butadiene rubber,preferably a styrene/butadiene copolymer rubber.

In practice, the coupling agent for the precipitated silica of therespective zones of the tread may be, for example, an alkoxysilylpolysulfide such as for example, a bis(3-trialkoxysilylalkyl)polysulfide wherein alkyl radicals for said alkoxy groups are selectedfrom one or more of methyl and ethyl radicals, preferably an ethylradical and the alkyl radical for said silylalkyl component is selectedfrom butyl, propyl and amyl radicals, preferably a propyl radical andwherein said polysulfide component contains from 2 to 8, with an averageof from 2 to 2.6 or an average of from 3.5 to 4, connecting sulfur atomsin its polysulfidic bridge, preferably an average of from 2 to 2.6connecting sulfur atoms to the exclusion of such polysulfides havinggreater than 2.6 connecting sulfur atoms.

Representative of such coupling agents are, for example,bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to2.6 or an average of from 3.5 to 4, connecting sulfur atoms in itspolysulfidic bridge, sometimes preferably an average of from 2 to 2.6connecting sulfur atoms to the exclusion of abis(3-triethoxysilylpropyl) polysulfide containing an average of greaterthan 2.6 connecting sulfur atoms in its polysulfidic bridge.

Such coupling agent may, for example, be added directly to the elastomermixture or may be added as a composite of precipitated silica and suchcoupling agent formed by treating a precipitated silica therewith or bytreating a colloidal silica therewith and precipitating the resultingcomposite.

In practice, the synthetic amorphous silica (precipitated silica) may beaggregates of precipitated silica, which is intended to includeprecipitated aluminosilicates as a co-precipitated silica and aluminum.

Such precipitated silica is, in general, well known to those havingskill in such art. For example, such precipitated silica may beprecipitated by controlled addition of an acid such as, for example,hydrochloric acid or sulfuric acid, to a basic solution (e.g. sodiumhydroxide) of a silicate, for example, sodium silicate, usually in thepresence of an electrolyte, for example, sodium sulfate. Primary,colloidal silica particles typically form during such process whichquickly coalesce to form aggregates of such primary particles and whichare then recovered as precipitates by filtering, washing the resultingfilter cake with water or an aqueous solution, and drying the recoveredprecipitated silica. Such method of preparing precipitated silica, andvariations thereof, are well known to those having skill in such art.

The precipitated silica aggregates preferably employed in this inventionare precipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate and mayinclude co-precipitated silica and a minor amount of aluminum.

Such silicas might usually be characterized, for example, by having aBET surface area, as measured using nitrogen gas, preferably in therange of about 40 to about 600, and more usually in a range of about 50to about 300 square meters per gram. The BET method of measuring surfacearea is described in the Journal of the American Chemical Society,Volume 60, Page 304 (1930).

The silica may also be typically characterized by having adibutylphthalate (DBP) absorption value in a range of about 50 to about400 cm³/100 g, and more usually about 100 to about 300 cm³/100 g.

Various commercially available precipitated silicas may be consideredfor use in this invention such as, only for example herein, and withoutlimitation, silicas from PPG Industries under the Hi-Sil trademark withdesignations Hi-Sil 210, Hi-Sil 243, etc; silicas from Rhodia as, forexample, Zeosil 1165MP and Zeosil 165GR, silicas from J. M. HuberCorporation as, for example, Zeopol 8745 and Zeopol 8715, silicas fromDegussa AG with, for example, designations VN2, VN3 and Ultrasil 7005 aswell as other grades of silica, particularly precipitated silicas, whichcan be used for elastomer reinforcement.

Representative examples of other silica couplers may beorganomercaptosilanes such as, for example, triethoxy mercaptopropylsilane, trimethoxy mercaptopropyl silane, methyl dimethoxymercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethylmethoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, andtripropoxy mercaptopropyl silane.

For this invention, it is desirable for physical properties of thesulfur cured rubber compositions of the tire tread zones to be aspresented in the following Table A.

TABLE A Intermedial zone rubber composition At least 4 units greaterthan the rebound (Zwick) value (100° C.), rubber of the lateral treadzones as a percent Intermedial zone rubber composition At least 15percent less than the Tan Delta value (1 Hertz, 15% strain, rubber ofthe lateral tread zones 100° C.) KPa Lateral zone rubber composition Atleast 20 percent greater than tear resistance, 95° C., the rubber of theintermedial in Newtons tread zone

The tear resistance may be determined, for example, by ASTM D1876-1taken with DIN 53539 using a 5 mm wide tear width provided by alongitudinal open space, sometimes referred to as a window, cut orotherwise provided, in the film positioned between the two rubber testpieces where the window provides a geometrically defined area, namelythe tear width, for portions of two rubber test pieces to be pressed andcured together after which the force to pull the test pieces apart ismeasured.

In practice, the invention the rubber compositions for the tire treadcomponents may be prepared in a sequential series of at least twoseparate and individual preparatory internal rubber mixing steps, orstages, in which the diene-based elastomer is first mixed with theprescribed carbon black and/or silica in a subsequent, separate mixingstep and followed by a final mixing step where curatives are blended ata lower temperature and for a substantially shorter period of time.

It is conventionally required after each mixing step that the rubbermixture is actually removed from the rubber mixer and cooled to atemperature of less than 40° C. and, for example, in a range of about40° C. to about 20° C. and then added back to an internal rubber mixerfor the next sequential mixing step, or stage.

The forming of a tire component is contemplated to be by conventionalmeans such as, for example, by extrusion of rubber composition toprovide a shaped, unvulcanized rubber component such as, for example, atire tread. Such forming of a tire tread is well known to those havingskill in such art.

It is understood that the tire, as a manufactured article, is preparedby shaping and sulfur curing the assembly of its components at anelevated temperature (e.g. 140° C. to 180° C.) and elevated pressure ina suitable mold. Such practice is well known to those having skill insuch art.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials, asherein before discussed, such as, for example, curing aids such assulfur, activators, retarders and accelerators, processing additives,such as rubber processing oils, resins including tackifying resins,silicas, and plasticizers, fillers, pigments, fatty acid, zinc oxide,waxes, antioxidants and antiozonants, peptizing agents and reinforcingmaterials such as, for example, carbon black. As known to those skilledin the art, depending on the intended use of the sulfur vulcanizable andsulfur vulcanized material (rubbers), the additives mentioned above areselected and commonly used in conventional amounts.

Typical amounts of fatty acids, normally used, may be comprised ofstearic acid which may also include at least one of palmitic and oleicacids, which comprise about 0.5 to about 3 phr. Typical amounts of zincoxide comprise about 1 to about 5 phr. Typical amounts of waxes compriseabout 1 to about 5 phr. Often microcrystalline waxes are used. Typicalamounts of peptizers comprise about 0.1 to about 1 phr. Typicalpeptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

The vulcanization is conducted in the presence of a sulfur vulcanizingagent. Examples of suitable sulfur vulcanizing agents include elementalsulfur (free sulfur) or sulfur donating vulcanizing agents, for example,an amine disulfide, polymeric polysulfide or sulfur olefin adducts.Preferably, the sulfur vulcanizing agent is elemental sulfur. As knownto those skilled in the art, sulfur vulcanizing agents are used in anamount ranging from about 0.5 to about 4 phr, or even, in somecircumstances, up to about 8 phr, with a range of from about 1.5 toabout 2.5, sometimes from about 2 to about 2.5, being preferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. Conventionally and preferably, a primary accelerator(s) isused in total amounts ranging from about 0.5 to about 4, preferablyabout 0.8 to about 2.5, phr. In another embodiment, combinations of aprimary and a secondary accelerator might be used with the secondaryaccelerator being used in smaller amounts (of about 0.05 to about 3 phr)in order to activate and to improve the properties of the vulcanizate.Combinations of these accelerators might be expected to produce asynergistic effect on the final properties and are somewhat better thanthose produced by use of either accelerator alone. In addition, delayedaction accelerators may be used which are not affected by normalprocessing temperatures but produce a satisfactory cure at ordinaryvulcanization temperatures. Vulcanization retarders might also be used.Suitable types of accelerators that may be used in the present inventionare amines, disulfides, guanidines, thioureas, thiazoles, thiurams,sulfenamides, dithiocarbamates and xanthates. Preferably, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator is preferably a guanidine, dithiocarbamate orthiuram compound.

The mixing of the rubber composition can preferably be accomplished bythe aforesaid sequential mixing process. For example, the ingredientsmay be mixed in at least three stages, namely, at least twonon-productive (preparatory) stages followed by a productive (final) mixstage. The final curatives are typically mixed in the final stage whichis conventionally called the “productive” or “final” mix stage in whichthe mixing typically occurs at a temperature, or ultimate temperature,lower than the mix temperature(s) of the preceding non-productive mixstage(s). The terms “non-productive” and “productive” mix stages arewell known to those having skill in the rubber mixing art.

Example I

Proposed rubber compositions were prepared for use for the intermedialand lateral tread zone rubber layers for the tire of this invention. Theproposed intermedial tread zone rubber composition is referred in thisExample as rubber Sample A.

The proposed lateral tread zone rubber composition is referred in thisExample as rubber Sample B.

The basic rubber composition formulations are shown in Table 1 and theingredients are expressed in terms of parts by weight per 100 partsrubber (phr) unless otherwise indicated.

The rubber composition may be prepared by mixing the elastomers(s)without sulfur and sulfur cure accelerators in a first non-productivemixing stage (NP-1) in an internal rubber mixer, for example, for about4 minutes to a temperature of, for example, of about 160° C. If desired,the rubber mixture may then mixed in a second non-productive mixingstage (NP-2) in an internal rubber mixer, for example, for about 4minutes to a temperature of, for example, about 160° C. with or withoutadding additional ingredients. The resulting rubber mixture may thenmixed in a productive mixing stage (PR) in an internal rubber mixer withsulfur and sulfur cure accelerator(s), for example, for about 2 minutesto a temperature of, for example, about 110° C. The rubber compositionmay then sheeted out and cooled to, for example, below 50° C. betweeneach of the non-productive mixing steps and prior to the productivemixing step. Such rubber mixing procedure is well known to those havingskill in such art.

The following Table 1 presents basic rubber formulations for proposedintermedial tire tread zone (rubber Sample A) and peripheral tire treadzone (rubber Sample B) rubber compositions for the zoned tread of thisinvention.

TABLE 1 (Intermedial and Lateral Tread Cap Zones) Parts (phr) A(Intermedial) B (Lateral) Non-productive Mix Step (NP1) Natural cis1,4-polyisoprene rubber 35 35 (TTR20) Cis 1,4-polybutadiene rubber¹ 6565 Carbon black (N121) 35 35 Silica, precipitated² 15 15 Silica couplingagent³ 2 0 Composite of silica coupling agent and 0 2 carbon black(50/50 weight ratio)* ⁴ Wax microcrystalline and paraffin 1.5 1.5 Fattyacid⁵ 2 2 Antioxidants 4 4 Zinc oxide 3 3 Final Mix Step (PR) Sulfur 1.10.9 Accelerator(s)⁶ 1.6 1.5 *Therefore 1 phr of coupling agent and 1 phrrubber reinforcing carbon black. ¹Cis 1,4-polybutadiene rubber (saidorganic solvent solution polymerized 1,3-butadiene monomer in thepresence of a neodymium catalyst) as CB25 ™ from the Lanxess Companyhaving a Tg of about −105° C. and heterogeneity index in a range of fromabout 1.5/1 to about 2.2/1. ²Precipitated silica as Zeosil ™ Z1165 MPfrom the Rhodia Company ³Silica coupling agent comprised ofbis(3-triethoxysilylpropyl) polysulfide having an average of from about2 to about 2.6 connecting sulfur atoms as Si266 ™ from Evonic ⁴Composite of silica coupling agent and carbon black (carrier) in a 50/50weight ratio where said coupling agent is comprised ofbis(3-triethoxysilylpropyl) polysulfide having an average of from about2 to about 2.6 connecting sulfur atoms as Si266 ™ from Evonic ⁵Mixturecomprised of stearic, palmitic and oleic acids ⁶Sulfenamide withdiphenyl guanidine sulfur cure accelerators with retarder as needed

The following Table 2 represents the uncured and cured behavior andvarious physical properties of the rubber compositions for theintermedial (rubber Sample A) and lateral (rubber Sample B) tire treadzone rubber layers based upon the basic formulations illustrated inTable 1.

TABLE 2 Properties A (Intermedial) B (Lateral) RPA (Rubber ProcessAnalyzer) test¹ Dynamic storage modulus (G′) Cured rubber G′ (1 Hertz,10% strain, 1.79 1.49 100° C.), KPa Tan delta (1 Hertz, 10% strain, 100°C.) 0.091 0.122 Stress-strain, ATS² Tensile strength (MPa) 21.2 20.8Elongation at break (%) 461 529 300% modulus, ring, (MPa) 12.1 9.66Rebound (Zwick)  23° C. 59 55 100° C. 69 64 Shore A Hardness  23° C. 6563 100° C. 61 58 Tear Strength (tear resistance)³, N At 95° C. 88 121Abrasion rate (mg/km), Grosch⁴ High severity (70N), 12° slip angle, 369368 disk speed = 20 km/hr., distance = 250 meters ¹RPA, rubber propertyanalytical instrument ²Automated Test System instrument (ATS), InstronCorporation, which incorporates a number of tests in one analyticalsystem and reports data from the tests such as, for example, ultimatetensile strength, ultimate elongation, modulii and energy to break data.³Data obtained according to a tear strength (peal adhesion), or tearresistance test. The tear resistance may be determined by ASTM D1876-01taken with DIN 53539 using a 5 mm wide tear width provided by alongitudinal open space, sometimes referred to as a window, cut orotherwise provided, in the film positioned between the two rubber testpieces where the window provides a geometrically defined area, namelytear width, for portions of two rubber test pieces to be pressed andcured together after which the ends of the two test pieces are pulledapart at right angles (90° + 90° = 180° to each other) and the force topull the test pieces apart is measured. An Instron instrument may beused to pull the rubber pieces apart using an Instron instrument at 95°C. with the force required being reported as Newtons force. ⁴The Groschhigh severity abrasion rate may be conducted on an LAT-100 Abrader andis measured in terms of mg/km of rubber abraded away. The test rubbersample is placed at a slip angle under constant load (Newtons) as ittraverses a given distance on a rotating abrasive disk (disk from HBSchleifmittel GmbH). In practice, a high abrasion severity test may berun, for example, at a load of 70 Newtons, 12° slip angle, disk speed of20 km/hr and distance of 250 meters.

It is seen in Table 2 that the Experimental rubber Sample A (rubbercomposition proposed for the intermedial tread zone) and Experimentalrubber Sample B (rubber composition proposed for the lateral treadzones) fulfilled the beneficially desired physical propertyrelationships presented in Table A for 100° C. hot rebound, and tearresistance (95° C.) values.

In Table 2 it is seen that the rebound value for rubber Sample A(proposed intermedial tread zone rubber composition) was greater thanthe for rubber Sample B (proposed peripheral tread zone rubbercomposition) which is indicative of beneficially lower hysteresis whichin turn is predictive of a beneficially lower rate of internal heatgeneration in the intermedial tread zone rubber composition as well aspredictively beneficial reduction of rolling resistance for the tirewith a resulting predictive fuel economy for a vehicle using such tires.

Further, in Table 2 it is seen that Tear Resistance for rubber Sample B(proposed lateral tread zone rubber composition) was beneficiallysignificantly greater than for rubber Sample A (proposed intermedialtread zone rubber composition).

Further, it is seen in Table 2 that the high severity Grosch rates ofabrasion for both rubber Sample A (proposed intermedial tread zonerubber) and rubber Sample B (lateral tread zone rubber) are similar,which is a desirable feature.

Further, it is seen in Table 2 that the tangent delta (tan delta) valuefor rubber Sample B (proposed lateral tread zone rubber) is greater thanfor rubber Sample A (proposed intermedial tread zone rubber). Such tandelta properties, taken with the aforesaid rebound properties are afurther indication of lower hysteresis, lower internal heat generationduring tire service for the intermedial tread rubber zone as well as theaforesaid predictive beneficial promotion of reduction in tire rollingresistance for increased vehicular fuel economy.

In summary and conclusion, a tire is provided with a configuredcircumferential tread zones to provide a running surface with zoneshaving similar rates of abrasion resistance but with lower hysteresis inthe intermedial tread zone which extends axially outward beneath thehigher hysteresis lateral tread zones for a purpose of maximizing suchlower hysteresis for the tread and with a higher tear resistance for thelateral tread rubber zone to promote resistance to groove surfacecracking in tread groove(s) contained in the lateral tread zones.

Such innovative tread configuration is intended to promote lower rollingresistance for the tire tread across the width of the tread by theextended intermedial tread zone which extends axially outward beneaththe lateral tread zones and to beneficially promote tear resistance forthe outlying lateral tread zones, the combination of which is consideredto be a significant departure from past practice.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:
 1. A tire is provided having a circumferentialrubber tread composed of a cap/base configuration comprised of an outertread cap rubber layer with a lug and groove configuration with theouter portions of the tread lugs providing the running surface of thetread, and a tread base rubber layer underlying the outer tread caprubber layer; wherein the outer tread cap rubber layer is composed ofthree circumferential load bearing zones comprised of an intermedialtread zone rubber layer positioned between and extending beneath twolateral tread zone rubber layers to thereby underlie the lateral treadzone rubber layers and overlay the tread base rubber layer to thereforestratify the lateral tread zone rubber layers as being separated fromeach other and from the tread base rubber layer; wherein outer surfacesof the tread lugs of the intermedial tread zone rubber layer and lateralstratified tread zone rubber layers comprise the running surface of thetread; wherein a peripheral rubber layer of the tread is provided whichis comprised of a radial extension of a tire sidewall rubber layercontaining at least about 40 phr of rubber reinforcing carbon blackwhich extends radially outward from the tire sidewall to form aperipheral rubber layer of the tread which extends to and includes aportion of the running surface of the tire; wherein rubber compositionof the intermedial tread zone rubber layer has a 100° C. hot reboundproperty greater than the 100° C. hot rebound property of the rubbercomposition of the stratified tread rubber layers.
 2. The tire of claim1 wherein the value of the 100° C. hot rebound property of theintermedial tread zone rubber composition is at least about 4 unitsgreater than the 100° C. hot rebound property value of the stratifiedtread zone rubber composition.
 3. The tire of claim 1 wherein the 100°C. hot rebound value of the intermedial tread zone rubber composition isin arrange of from about 60 to about 80 percent and the 100° C. hotrebound value of the rubber composition of the stratified tread zonerubber composition is in a range of from about 56 to about 76 so long asthe 100° C. rebound values differ by at least about 4 units.
 4. The tireof claim 1 wherein the stratified lateral tread zone rubber compositionhas an at least 20 percent greater tear resistance property than theintermedial tread zone rubber and where the intermedial and stratifiedlateral tread zones are configured with lugs and intervening grooveswith each stratified tread zone containing at least one tread groove. 5.The tire of claim 1 wherein the particulate reinforcement of the rubbercompositions of the intermedial tread rubber zone and lateral treadrubber zones are the same or different and comprised of rubberreinforcing carbon black and/or precipitated silica reinforcement solong as the 100° C. hot rebound property of the rubber composition ofthe intermedial tread rubber zone is greater than the 100° C. hotrebound property of the rubber composition of the stratified lateralrubber zones.
 6. The tire of claim 1 wherein the rubber compositions ofthe intermedial tread rubber zone and stratified later tread rubberzones are the same or different so long as the 100° C. hot reboundproperty of the rubber composition of the intermedial tread rubber zoneis greater than the 100° C. hot rebound property of the rubbercomposition of the stratified lateral rubber zones.
 7. The tire of claim6 wherein the rubber compositions of the intermedial tread rubber zoneand stratified lateral tread rubber zones are the same or different solong as the 100° C. hot rebound property of the rubber composition ofthe intermedial tread rubber zone is greater than the 100° C. hotrebound property of the rubber composition of the stratified lateralrubber zones.
 8. The tire of claim 1 wherein the rubber composition ofthe intermedial zone and/or stratified lateral tread zones aresilica-rich in a sense of containing at least 40 phr of precipitatedsilica and a maximum of 30 phr of rubber reinforcing carbon black andthereby presenting a significant degree of insulative electricalresistance for the intermedial and/or lateral rubber layer zones so longas the 100° C. hot rebound property of the intermedial tread zone isgreater than the 100° C. hot rebound property of the stratified treadzones, wherein the peripheral carbon black-rich rubber sidewallextension provides a path of least electrical resistance between thetire carcass and tread running surface.
 9. The tire of claim 1 whereinthe rubber composition of the intermedial zone and/or stratified zonesare carbon black rich in a sense of containing at least 40 phr of rubberreinforcing carbon black zones so long as the 100° C. hot reboundproperty of the intermedial tread zone is greater than the 100° C. hotrebound property of the stratified tread zones.
 10. The tire of claim 1wherein the span of the running surface of the intermedial tread zonerubber layer axially spans from about 30 to about 80 percent of therunning surface of the tread cap rubber layer and the two lateral treadrubber zone rubber layers collectively span from about 20 to about 70percent of the running surface of the tread cap rubber layer where saidspan of running surface of the tread includes the running surfaces ofthe tread lugs and widths of the tread grooves between the tread lugs.11. The tire of claim 10 wherein the span of running surfaces of the twoindividual lateral tread zones are of substantially equal widths. 12.The tire of claim 10 wherein the span of running of the two individualstratified lateral tread zones is asymmetrical in a sense that they areof unequal widths.
 13. The tire of claim 1 wherein the Grosch highseverity abrasion rate of the rubber compositions of the runningsurfaces of the intermedial tread zone running surface and stratifiedlateral tread zone are desirably similar.
 14. The tire of claim 1wherein the stratified lateral tread zones, intermedial tread zone andunderlying tread base are co-extruded together to form an integral andunified tread composite.
 15. The tire of claim 1 wherein the rubber ofthe intermedial, tread cap zone has a lower tan delta value at 10percent strain (100° C.) than the rubber of the two stratified lateraltread cap zones.
 16. The tire of claim 1 wherein the tear resistance(Newtons at 95° C.) of the stratified lateral tread zones is at least 20percent greater than the tear resistance of the rubber composition ofthe intermedial tread zone.
 17. The tire of claim 1 wherein theintermedial and stratified lateral tread zones are configured with lugsand intervening grooves with the stratified tread zones each containingat least one tread groove.